acromioclavicular joint

joint

[joint]

the site of the junction or union of two or more bones of the body; its primary function is to provide motion and flexibility to the frame of the body. Some are immovable, such as the sutures where segments of bone are fused together in the skull. Others, such as those between the vertebrae, are gliding joints and have limited motion. However, most joints allow considerable motion. The most common type are the synovial joints, which have a complex internal structure, composed not only of ends of bones but also of ligaments, cartilage, the articular capsule, the synovial membrane, and sometimes bursae.

acromioclavicular joint the point at which the clavicle joins with the acromion.

ball-and-socket joint a synovial joint in which the rounded or spheroidal surface of one bone (the “ball”) moves within a cup-shaped depression (the “socket”) on another bone, allowing greater freedom of movement than any other type of joint. See illustration. Called also polyaxial or spheroidal joint.

composite joint (compound joint) a type of synovial joint in which more than two bones are involved.

condylar joint (condyloid joint) one in which an ovoid head of one bone moves in an elliptical cavity of another, permitting all movements except axial rotation; this type is found at the wrist, connecting the radius and carpal bones, and at the base of the index finger. See illustration.

gliding joint a synovial joint in which the opposed surfaces are flat or only slightly curved, so that the bones slide against each other in a simple and limited way. The intervertebral joints are this type, and many of the small bones of the wrist and ankle also meet in gliding joints. Called also arthrodial joint and plane joint.

hinge joint a synovial joint that allows movement in only one plane, forward and backward. Examples are the elbow and the interphalangeal joints of the fingers. The jaw is primarily a hinge joint but it can also move somewhat from side to side. The knee and ankle joints are hinge joints that also allow some rotary movement. See illustration. Called also ginglymus.

pivot joint a synovial joint in which one bone pivots within a bony or an osseoligamentous ring, allowing only rotary movement; an example is the joint between the first and second cervical vertebrae (the atlas and axis). See illustration. Called also rotary or trochoid joint.

sacroiliac joint the joint between the sacrum and ilium in the lower back; see also sacroiliac joint.

saddle joint a synovial joint whose movement resembles that of a rider on horseback, who can shift in several directions at will; there is a saddle joint at the base of the thumb, so that the thumb is more flexible and complex than the other fingers but is also more difficult to treat if injured.

synovial joint a specialized joint that permits more or less free movement, the union of the bony elements being surrounded by an articular capsule enclosing a cavity lined by synovial membrane. Called also articulation and diarthrosis. A capillary network in the synovial membrane provides nutrients and synovial fluid to nourish and lubricate the joint space. Strong fibrous bands or cords (ligaments) give strength and security to synovial joints. The majority of the body's joints are of this type. They are divided into five types according to structure and motion: ball and socket, gliding, saddle, hinge, and pivot.

a·cro·mi·o·cla·vic·u·lar joint

acromioclavicular joint

The joint plane between the medial margin of the acromion of the scapula and the lateral margin of the clavicle. The AJ is formed by the acromioclavicular ligament, the articular disk and coracoclavicular ligament, which has 2 portions, the trapezoid and conoideum.

a·cro·mi·o·cla·vic·u·lar joint

(ă-krō'mē-ō-klă-vik'yū-lăr joynt) [TA]

A plane synovial joint between the acromial end of the clavicle and the medial margin of the acromion.

acromioclavicular joint

The joint between the outer end of the collar-bone (clavicle) and the ACROMION process on the shoulder-blade (scapula).

Figure 1: Ascending nerve pathways and proprioceptive reflex arcs, represented in diagrammatic sections of the brain and spinal cord. Shown on the right: those serving the sensations listed. Shown on the left: reflex pathways for skeletal muscle control. (A) From a muscle spindle, to a synapse with an alpha motor neuron, and a branch to the brain. (B) From a tendon organ, inhibitory branch (broken line) to an alpha motor neuron, and a branch to the brain.

acromioclavicular joint

the small synovial joint above the shoulder, between the outer end of the clavicle and the acromion process of the scapula, linking them to form the shoulder girdle. Parts of the trapezius and deltoid muscles are attached to the joint capsule. Commonly injured in contact sports especially rugby. Figure 1.

2,14,31-33) Operative intervention is often reserved for the types IV, V, and VI injuries, which involve a higher-energy mechanism that results in significant instability of the acromioclavicular joint.

The most common source of pain in the shoulder was found to be soft tissue lesions (81%), of which the bulk were lesions of the rotator cuff (65%), periscapular soft tissue (11%), acromioclavicular joint pain (10%) and cervical referred pain (5%).

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